Tissue sample data suggests that malignant mammary tumors have electrical properties which mimic those typically found in high-water content tissues such as muscle whereas the surrounding normal breast is more representative of low-water content fatty tissues. Presumably, the increased blood volume associated with the neovascularization in the rapidly proliferating tumor periphery is partly responsible for the increased water content which establishes a significant contrast mechanism to which microwave illumination is particularly sensitive. It has also been hypothesized that the progressive replacement of fat lobules with fibroblastic proliferation and epithelial cells and the alterations that occur at transformed cell surfaces produce ultrastructural changes in neoplastic breast tissue which cause the observed difference in electrical properties. In fact, the normal and malignant human tissues of the same histological type, the largest difference in electrical properties. In fact, for normal and malignant human tissues of the same histological type, the largest difference in electrical properties has been observed in the mammary gland relative to colon, kidney, liver, lung and muscle. This data coupled with recent advances in model-based near-field imaging concepts provide a compelling rationale to pursue microwave imaging of breast tissue for diagnostic-advantage. Project III will extent previously developed near-field microwave imaging principles and concepts of high frequency (0.5-3 GHz) electromagnetic interrogation of breast tissue for the purpose of generating spatially-resolved electrical property distributions The increase in operating frequency range can readily occur because of the largely translucent nature of breast tissue to microwave illumination and the overall small physical dimensions of the imaging region of interest. However, changing the operating frequency range drives both hardware and software design considerations which are the focus of the developmental components of this project. The specific aims of Project III can be summarized as (1) to realize a prototype 32 channel high frequency (o.5-3GHz) data acquisition system for near-field microwave illumination, (2) to implement, in conjunction with the Computational Core, new model-based image reconstruction advances including multi-component objective function minimizations, adaptive dual meshing, antenna coupling models and multi-spectral reconstructions and explore imaging method extensions, in particular,, with regard to three-dimensional imaging, (3) to evaluate and optimize phantom imaging based on geometries relevant to clinical breast examination, (4) in conjunction with the Clinical Core, demonstrate the clinical feasibility of microwave breast imaging and initiate an evaluation of the efficacy of high frequency electromagnetic property imaging as a diagnostic tool in patients with normal and abnormal mammograms